Thanks for the plot update, also I think I like the idea of Mashou Captain America. Also also, I think I've got a theme song lined up for my character.
I presumed the 'propensity for high emotions' rationality given in the original anime had some kind of hold. I've only watched the original 13 episode series and first movie, I don't actually know the post-Madokami-ascension world so well, I presumed because all the same girls before the change also had to contract after, that there was no change in the contracting requirements. The only bits I hold any attachment to are 'know she was able to contract from young age' and 'parents work wealthy jobs', but those are also up for change if necessary.
Tinkering is more of a secondary for my character than a primary power. My character is still human in the time it takes to tinker stuff. Perhaps fifteen seconds and modify an already existing pistol to fire a single type of magical bolt, or patch up an already existing weapon, but that's vastly different from conjuring entire turrets out of the aether. Most of her magic is useless on the battlefield without preparation time.
Her primary power is 'understanding' magic, both the wraiths she fights, and the magic of other mashou, which she can use to either amplify them with her own magic/advice on optimization of use, or dismantle/neutralize (either through direct dispelling, or indirectly such as knowing it has X or Y limit).
Also Nadica's something like 60 years her senior, and their personalities would likely clash, but that's part of the fun. I can imagine the protesting against the 'young whippersnapper'.